An Incompetent Woman Wants to Be a Villainess ~The Young Lady Who Married as a Substitute for Her Stepsister Didn't Notice the Duke's Doting~ is a Manga/Manhwa/Manhua in (English/Raw) language, ROMANCE series, english chapters have been translated and you can read them here. You are reading chapters on ManhwaZ fastest updating comic site. The Summary is
Avril is a young woman of exceptional ability who was mistreated and labeled "incompetent" by her family. Avril marries into the family of an "old, lustful duke" in place of her half-sister, but the duke, Dylan, is actually a beautiful young man who is the complete opposite of what he is rumored to be. He wants to marry a "villainess," and a contractual divorce her after three years is perfect for Avril's future freedom. The people around her are bewildered by the mysterious "brilliant woman" who plays the role of a "villainess" with gusto, but they are gradually drawn to her..